1. Field of the Invention
This invention relates to a self-igniting reciprocating internal combustion engine for direct fuel injection and for use as a two-stroke-cycle or four-stroke-cycle engine. 2. Description of the Prior Art
In internal combustion engines it is known to subdivide the combustion chamber in order to improve the quality of the mixture being formed during the compression stroke by a high turbulence. A distinction can be made between the so-called prechamber process, the swirl chamber process, the air chamber process and the direct fuel injection process.
In the prechamber process, a prechamber is provided, which has a volume of about 20% of the compression volume because fuel is injected only into the prechamber. The deficiently of air in said chamber at the beginning of the ignition or combustion has the undesirable results that carbon black is formed, that the fuel is not completely utilized and, in particular, that an afterburning takes place during the expansion stroke. A further disadvantage resides in the losses, which are mainly caused by hydraulic heat transfer that is due to the division of the combustion chamber and which involve a fairly high fuel consumption.
In the swirl chamber process a swirl chamber is used, which has a volume of up to 50% of the compression volume. Fuel is injected only into the swirl chamber and the combustion pressure is initially generated in the swirl chamber and is then transferred to the main compression spaces through the flash passage, through which the swirl chamber communicates with the main compression chamber, in which the pressure is applied to the piston. Afterburning may occur in that case too and the division of the combustion chamber undesirably results in high losses owing to the heat transfer and, in a fairly high specific fuel consumption.
In the air chamber process there is no injection of fuel into the air chamber but fuel is injected in or opposite to the overflow direction in a funnel-shaped flash passage. Just as in the prechamber process and the swirl chamber process, the mixture is formed in the main combustion chamber also by the burning gas stream. A disadvantage of the air chamber process resides in the somewhat rough operation of the engine and in the high fuel consumption.
In the direct fuel injection process the mixture is formed by the injection of fuel and is less desirable than in the above-mentioned processes because there is no turbulence or only a low turbulence. Besides, the air demand is high and results in a poor utilization of the air and the mean effective is not as high as in prechamber and swirl chamber engines. Another disadvantage resides in the sudden ignition and combustion of the mixture and the resulting rough operation of the engine. Besides, the high fuel injection pressures used in the fuel injection process require powerful fuel pumps.
Each of the processes mentioned hereinbefore has specific disadvantages and represents a comprise because one source of losses or another is intentionally tolerated in the desire to minimize the total losses. It has not been possible thus far to minimize all losses and, at the same time, to meet present-day requirements as regards environmental compatibility, improved efficiency, and a simple structure of the engine unit. These remarks are also applicable to the high compression ratio, which was previously required and which is inconsistent with the requirements for a satisfactory and economical operation, which would require low compression ratios. The high compression ratio previously employed calls for high strengths, which can be achieved only in heavy engines. On the other hand, the use of lower compression ratios would permit engines to be built which are lighter in weight.
Published German Patent Application 15 26 290 discloses an externally ignited engine having a relatively low compression ratio and comprising a main combustion chamber, an ignition chamber and a flash passage. The volume of the ignition chamber is about 7.5% of the volume of the main combustion chamber. The ignition chamber contains a spark plug or heater. Fuel is injected through a multi-jet fuel injector, by which a first fuel jet is directly injected through the flash passage into the ignition chamber and a second fuel jet is injected against the surface of recess in the piston. In connection with external ignition by means of the spark plug which is provided, it has been stated only broadly that fuel may be injected into the ignition chamber before the main quantity of fuel is injected into the main combustion chamber. A disadvantage of that concept resides in the complicated design and control of the fuel injector. Besides, the fuel must be injected under a high pressure so that an engine which would be light in weight cannot be designed.
Published German Patent Application 29 22 683 discloses an air-compressing self-igniting internal combustion engine, which is operated by the swirl chamber process and comprises a fuel injector for injection fuel into the swirl chamber and a separate fuel injector for injecting fuel into the main combustion chamber. The two fuel injectors are supplied with fuel from a single fuel injection pump through a control valve, by which the supply of fuel to the second fuel injector is controlled in dependence on load or speed. In that case a disadvantage of that system resides in that it is highly susceptible to trouble and that a powerful fuel injection pump is required.
Published German 40 33 843 discloses a two-component internal combustion engine, wherein natural gas or other gaseous fuels are to be ignited by a small pilot quantity. This is effected by introducing a small pilot quantity of Diesel gas or another inflamable fuel in a self-igniting chamber. Burning gas or natural gas is sucked in through an inlet valve into the cylinder and is then compressed therein. There is no usual Diesel injection. Though there is an injecting nozzle in the middle of the cylinder head this is not for working, but only for starting, since, after start, operation is switched over to natural gas operation. Moreover, with this igniting internal combustion engine there is no preheating in an igniting chamber and, therefore, there is a high compression and, necessarily, a massive design of cylinder head, which simultaneously results in an increase of the weight of the internal combustion engine which is not advantageous. Finally, there is only one injecting pump, which is provided only for the starting phase.